Environmental Gradients and Hen Spatial Distribution in a Cage-Free Aviary System: Internet of Things-Based Real-Time Monitoring for Proactive Management

This study assessed environmental gradients at different heights in a multi-tiered aviary and their relationship with hen spatial distribution. Two pens of an experimental aviary housing 225 Novogen hens (Novogen S.A.S., Plédran, France) each were monitored when their hens were 32-52 weeks old over three periods (January, March, and June). The environmental conditions (humidity, sound intensity, NH₃, CO₂, and particulate matter; PM: PM₁, PM_2.5, PM₄, and PM₁₀) were continuously recorded every 10 min, 24 h per day, at three heights (floor and middle and upper tiers) using an IoT-based system. Hen distribution was analysed using video recordings from 04:00 to 20:00, scanning 15 min for every 30 min of video. On the whole, the air quality was always consistent with the recommended values for laying hens. The middle tier, where nests were located, exhibited a higher humidity and CO₂ and PM concentration compared to the upper tier and floor, suggesting reduced airflow. This result can be related to the reduced length of the experimental barn containing only one row of equipment, which likely affected air circulation and distribution compared to what happens in commercial barns with several rows and a length over 50 m. Hen distribution varied during the day, with hen presence on the floor being highest in the midday (58% of hens) and correlated with increased particulate matter (r = 0.57-0.60; <i>p</i> < 0.001) and NH₃ concentrations (r = 0.33; <i>p</i> < 0.001). Hens occupied the upper tier more in June (34% vs. 24% in January; <i>p</i> < 0.001), correlating with lower humidity and PM levels. Understanding daily and seasonal changes in environmental gradients at different aviary tiers could help optimise ventilation schemes and air quality control and ensure hen welfare, health, and production throughout the laying cycle.